The invention relates to a master-batch on a polyamide base, and to its use.
In the plastics processing industry the use of master-batches is widely known for achieving desired properties such as pigmentation, anti-static provision, anti-blocking function, flow promotion, etc.
Master-batches are used as, in comparison to pure additives, they offer a series of advantages such as clean handling, precise metering, clearly reduced risk of de-mixing, simple combination of various additives and rapid uniform distribution of the additives in the polymer compound.
As a rule there is used, as a carrier material for the additives in the master-batch, the base material coming into consideration in the on a polyamide base, or a material compatible with this base material.
Although master-batches are also widely used in processing polyamides, and provide a satisfactory solution to partial problems, until now no master-batch could be prepared based on a polyamide which can fulfil the following problem solutions and market requirements in one single master-batch material:
a) carrier material and base material identical and compatible
b) anti-blocking functions
c) increased slip property of the article produced (improved surface slip)
d) additives resistant to sterilisation.
Until the present, a polyamide master-batch has been known from U.S. Pat. No. 5,109,049 (American National Can Company), which offers anti-blocking functions, but affords no advantages as regards slip properties.
There is described by the company Hoechst in EP 0 662 534 A1 a special polyamide master-batch which is preferably suitable for pigmenting aromatic polyamide fibres and shaped structures.
Until today no single master-batch could be found on the market which is particularly suitable for the manufacture of films, and unifies the following properties in one single product:
extremely good compatibility with the base material and admixture without impairing the most important properties of the film, such as mechanical strength, barrier effect, optical properties
uniform crystallinity of the film
outstanding slip property of the film
assured anti-blocking properties
resistance to sterilisation
permitted for foodstuffs.
With respect to the improved slip property of films, these properties are increasingly demanded by the market, as new automatic packaging machines, particularly for packaging meat and cheese, require a high degree of slip property in order to increase the machine cycle frequencies. In the new automatic packaging machines (deep-drawing systems), the maximum possible cycle frequencies are predetermined by the running or sliding capacity of the films.
The meat and cheese portions to be packaged are in addition becoming increasingly large and heavy, which imposes increased demands on the packaging films.
The market demands as a measurement value for the polyamide layer of packaging films a dynamic coefficient of friction (COF) of 0.2 in accordance with DIN 53375.
In addition to this low coefficient of friction, the market also demands that all the further abovenamed properties be likewise contained in a single master-batch.
If the entire required spectrum of properties has to be combined by various master-batches or also in combination with additives, this is extremely complex, often impossible, but certainly more cost-intensive, as this requires a correspondingly-designed infrastructure of the production systems.
It would be extremely desirable for the packaging industry and particularly for the manufacturers of packaging films to have for the production of polyamide films one single master-batch which produces films with the following advantages:
clear advantages in further processing of films due to better slip properties and shorter packaging cycles on packaging machines,
no tendency for the film to block, particularly in the case of copolyamides, which tend to adhere,
absolute reliability in sterilisation without uncontrolled blooming,
adjustment of the required film performances in dependence on the quantity of added master-batch,
master-batch formulation reliable with foodstuffs.
Proceeding from this point, it is the object of the present invention to propose a new master-batch which has good compatibility particularly with the base material, and leads to increased slip properties in the articles produced. The articles produced should further have an anti-blocking function. It is also desirable that the product should be resistant to sterilisation.
This object is achieved by providing a packaging film comprising a polyamide base and 1-8% of a master-batch, said master batch comprising: 60 to 95% by weight of compolyamide PA6/12 as a polyamide carrier material; 2 to 20% by weight of NNxe2x80x2ethylene-bis-fatty acid amide with a C18 fatty acid proportion of at least 60% as a slip additive; 1.5 to 10% by weight of micronized Mg3SinO10(OH)2as a nucleation agent; and 1.5 to 10% by weight of calcium carbonate as an anti-blocking agent. Additional advantageous developments are also disclosed herein.
Accordingly, the master-batch according to the invention contains 60 to 95% by weight of a polyamide carrier material and 2 to 20% by weight of NNxe2x80x2ethylene-bis-fatty amide, and proportions of additive materials supplemented up to 100% by weight.
It has become surprisingly apparent that by means of the end-products from the formulations described above, the desired properties such as slippery films, sterilisable films and anti-blocking properties can be achieved. In addition, a factor which could not be foreseen by the person skilled in the art is that all the properties may be realised simultaneously. It is thus possible for the first time, with the master-batch according to the invention, favourably to influence the end-product in a controlled manner with respect to various properties.
All the currently available polyamide types may in themselves be used as a polyamide carrier material. Preferably copolyamide PA 6/12, polyamide 6, polyamide 12 or amorphous polyamide such as polyamide 6I/6T are used as a polyamide carrier material. It has proved particularly favourable if copolyamides PA 6/12 with melting temperatures of 130 to 150xc2x0 C. are used as a polyamide carrier material. A decisive advantage of this copolyamide 6/12 is that in these polymers the melting point can be adjusted by the relationship of Caprolactam to Laurinlactam within a wide range, and thus a universal degree of application can be achieved.
An essential factor in the subject-matter of the Application is that 60 to 95% by weight of the polyamide carrier material described above is used exclusively in combination with a specially selected modified synthetic fatty amide wax, i.e. with 2 to 20% by weight of NNxe2x80x2ethylene-bis-fatty amide. It has proved advantageous if an NNxe2x80x2ethylene-bis-fatty amide is used with a C 18 fatty acid proportion of at least 60%, preferably with a C 18 fatty acid proportion of at least 90%. Only in this way is it possible for the films produced by the master-batch according to the invention to possess outstanding slip properties.
The master-batch formulation according to the invention, as described above, in addition contains proportions supplemented up to 100% by weight of additive materials, such for example as nucleation aids, anti-blocking aids, anti-oxidant aids and mastication aids. In this case the use of 1.5 to 10% Microtalk is preferred as a nucleation agent, and 1.5 to 10% calcium carbonate as an anti-blocking agent.
A particularly preferred master-batch formulation comprises 80 to 85% by weight PA 6/12, 5 to 10% by weight of NNxe2x80x2ethylene-bis-fatty amide, 5% by weight Microtalk and 5% by weight calcium carbonate. The abovementioned formulation leads in particular to products which have all the required properties.
The master-batches were produced on a commercially conventional double-shaft extruder, e.g. of the company Werner+Pfleiderer, Germany. The low-melting-point PA 6/12 carrier material, which required clearly lower extrusion temperatures than the polyamides with a higher melting point, proves particularly favourable. This results in low thermal stress on the admixed additives, so that they retain their efficiency to a maximum extent.